Spent nuclear fuel transport and/or storage casks (100-ton class) must maintain their structural integrity even when subjected to hypothetical transportation or handling accidents at storage facilities. For ductile cast iron (DCI) to be used as a cask containment boundary material, adequate fracture toughness and associated ductile behavior must be demonstrated at service temperatures and impact loading conditions of concern.

Six- and 8-in. (150- and 200-mm) thick compact tension (6TC[T] and 8TC[T]) specimens were extracted from three prototypic and two model casks and were tested. The results obtained in this study and the data obtained from another prototypic cask and six other model casks were analyzed statistically. The lower-bound fracture toughness trend curves for heavy-section DCI were finally established as a function of temperature.

Small specimens (for example, 1TC[T]), notched round bar tension, and U-notched Charpy specimens) were machined from the fractured halves of the 6TC(T) and 8TC(T) specimens and were tested under similar temperature and loading rate conditions. The relationship between the results from small specimens and those defining the lower-bound trend curves is also discussed. Fracture toughness prediction methods based on small specimen tests at specified temperature are proposed.